How critical is piston deck height & quench distance for an LS1?
11-13-2003, 10:57 PM
#1
How critical is piston deck height & quench distance for an LS1? In blueprinting my LS6 short block I noted that the piston sits 0.004" below the deck height and when I combine this with the correct GM head gaskets for my LS6 heads the quench distance appears to be 0.064". This seems awfully high to me for an LS1. Should I be decking the block surface to obtain a positive piston deck height above the block to decrease the quench distance? I plan on running static compression in the 11.8:1 range on pump gas.
11-14-2003, 12:07 AM
#2
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John, 0.064" quench is pretty high for your setup, especially if you are going to run that compression on pump gas.
I would shoot for around .040" quench. To achieve this, you can 0 deck the block and install a thinner head gasket.
BTW, what rod/piston combo are you using?
I would shoot for around .040" quench. To achieve this, you can 0 deck the block and install a thinner head gasket.
BTW, what rod/piston combo are you using?
11-14-2003, 01:06 AM
#3
Agreed. And on top of that it's going to increase when the engine warms up. That is too much quench distance in ANY motor. That's just begging for detonation. You can run the piston out of the hole.
Chris
Chris
11-14-2003, 07:53 AM
#6
BTW, what rod/piston combo are you using?
FWIW, the pistons came out of the hole .007" and I was using a .052" gasket on my solid roller forged motor for a .045" quench.
So is there a maximum recommended height above the block that the pistons should/could be to achieve somewhere around 0.040" total quench?
11-14-2003, 09:27 AM
#7
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.010 -.014
the 370 i built last were about .013 OUT of the hole.these gen lll motors are setup to pop up out of the at least .010 stock is right at that if i recall correctly. if you're .004 below the deck height, talk to diamond about your pistons or measure your actual rod length.
i hate to say it, but it sounds to me like something came out wrong. a rod length, or a pin position, ect.. best of luck to ya.
the 370 i built last were about .013 OUT of the hole.these gen lll motors are setup to pop up out of the at least .010 stock is right at that if i recall correctly. if you're .004 below the deck height, talk to diamond about your pistons or measure your actual rod length.
i hate to say it, but it sounds to me like something came out wrong. a rod length, or a pin position, ect.. best of luck to ya.
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11-14-2003, 09:35 AM
#8
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Deck Height or Deck Clearance:
This most important step consists of measuring the distance from the assembled piston tops to the surface of the block deck (deck clearance), and milling as necessary. The general feeling is that the total quench or squish distance should be about .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance. The quench area is the flat part of the piston that would contact a similar part of the head if you had .000 assembled quench height. In a running engine, the .040 quench height decreases to a close collision between the piston and the cylinder head. The shock wave from the near collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, averages the chamber temperature, reduces detonation and increases power. The shock wave also provides better fuel/air mixing, and this allows the fuel to ignite better and burn faster. A faster burning fuel charge means less timing is required for optimum power output. An example of this--a running 462 had a factory deck height of about .020, the deck was set to 0. There were no other significant changes to the engine (new rings and bearings, but same cam, heads, intake and exhaust systems). The optimum timing setting prior to the change was 34 degrees - that provided the fastest MPH and quickest ET. After the change to 0 deck, the optimum timing using the same Amoco gas changed to only 30 degrees total mechanical. Not only did the lowering the deck raise the CR by several tenths of a point, but by retarding the timing 4 degrees, it was possible to increase the CR even higher due to the optimum lower timing setting.
Note: Since it is the close spacing between the piston and cylinder that reduces the prospect of detonation, never add a shim/head gasket, or flat cut the pistons tops to reduce CR. If you have proper quench with 10 to 1 CR, and then reduce the CR to 9.5 by one of these two methods, you will create more ping with the 9.5 CR then you had with the 10 CR. By all means, deck the block first and under all circumstances when building an engine for optimum power output, and then determine what chamber volume will be needed in the heads to arrive at the final CR.
This most important step consists of measuring the distance from the assembled piston tops to the surface of the block deck (deck clearance), and milling as necessary. The general feeling is that the total quench or squish distance should be about .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance. The quench area is the flat part of the piston that would contact a similar part of the head if you had .000 assembled quench height. In a running engine, the .040 quench height decreases to a close collision between the piston and the cylinder head. The shock wave from the near collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, averages the chamber temperature, reduces detonation and increases power. The shock wave also provides better fuel/air mixing, and this allows the fuel to ignite better and burn faster. A faster burning fuel charge means less timing is required for optimum power output. An example of this--a running 462 had a factory deck height of about .020, the deck was set to 0. There were no other significant changes to the engine (new rings and bearings, but same cam, heads, intake and exhaust systems). The optimum timing setting prior to the change was 34 degrees - that provided the fastest MPH and quickest ET. After the change to 0 deck, the optimum timing using the same Amoco gas changed to only 30 degrees total mechanical. Not only did the lowering the deck raise the CR by several tenths of a point, but by retarding the timing 4 degrees, it was possible to increase the CR even higher due to the optimum lower timing setting.
Note: Since it is the close spacing between the piston and cylinder that reduces the prospect of detonation, never add a shim/head gasket, or flat cut the pistons tops to reduce CR. If you have proper quench with 10 to 1 CR, and then reduce the CR to 9.5 by one of these two methods, you will create more ping with the 9.5 CR then you had with the 10 CR. By all means, deck the block first and under all circumstances when building an engine for optimum power output, and then determine what chamber volume will be needed in the heads to arrive at the final CR.
11-14-2003, 01:17 PM
#14
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John, I agree with Vents. Double check your piston's compression height and rod length just to be sure. All the 6.125" rods and off the shelf 3.905" Diamond pistons I have used put the pistons above the deck pretty close to where the stock pistons are (which is ~.006-.007")
As for my motor, it could be run on pump gas taking it easy, but it did require a mix of race gas/93 octane when I really hammered on it. The chamber volume was 55cc (milled 5.3s). This put my compression pretty close to what you are shooting for.
The Cometics are available in many different thickneses.
As for my motor, it could be run on pump gas taking it easy, but it did require a mix of race gas/93 octane when I really hammered on it. The chamber volume was 55cc (milled 5.3s). This put my compression pretty close to what you are shooting for.
The Cometics are available in many different thickneses.
11-14-2003, 02:31 PM
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Thunder Racing carries both the Cometic and Felpro gaskets. They are not on the webpage as of yet, but they have many bore sizes/thicknesses in stock.
www.thunderracing.com
Jason
www.thunderracing.com
Jason
11-14-2003, 02:42 PM
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You can order the cometics from cometic directly. I am using a custom .041 set right now. From talking to fel pro directly they said that they only come in a stock height .052 inch.
11-14-2003, 02:51 PM
#19
I hate to be a dick but J-Rod you did not write that yourself. That is word for word from I believe SpeedOMotive's website. I'll have to look tonight to be sure. Own up to it, you copied and pasted.
Chris
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11-14-2003, 03:26 PM
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I didn't see J-Rod saying ANYWHERE that he wrote that. In fact, I was very much under the impression it was cut and pasted by the way it was formatted. He's not trying to take credit for it, he's just pasting relevent information. If you've read some of his other long posts, you'll realize he does these "information dumps" a lot.
Anyway, good subject matter....I'm learning a lot in this thread.
Anyway, good subject matter....I'm learning a lot in this thread.